If you go to Mr. Ford's machinist's tips site and follow it down you'll find this tip:http://www.frets.com/HomeShopTech/QuickTricks/RustRemoval/rustremov...
which I tried yesterday and it works amazingly well. I used an old 7.25" circular saw blade for the anode (the "piece of steel" in the article) as it has lots of surface area. After using it bust severe rust on the old pump housing that I've modified to take my new table saw motor I decided to hasten removal of the really thick corrosion (over 3/8" in some places) by doubling the voltage so I connected two "battery chargers" (really two high current DC power supplies I'd made) in series which gave me around 28VDC which really bubbled. Since I've got a great collection of old transformers of various kinds I think I'm going to cobble up a 48-50 VDC one just for this purpose as the DC supply can be unfiltered with lots of hum for rust busting so I don't need any filter caps only rectifiers. I could go higher with the voltage but 50V is considered the highest safe voltage to handle without worrying about electrocuting yourself. I may also experiment with other electrolytes (the baking soda the article - the piece you're removing the rust from becomes the cathode and this is a variation of the "sacrificial anode" technique) such as hydrochloric acid ("muriatic" acid) or oxalic acid. If acidic electrolytes don't seem to work better I may try lye or sodium carbonate to see if stronger alkalies work well. Anyhoo if you've got a battery charger I'd try it as while all the bubbling is impressive the actual current draw is tiny - the electrolyte seems to have a resistance of around 10 megaohms per 1/4" or so mixed at 1/8 box of baking soda/two gallons of warm water - so most any charger or a charged old battery would work and the amount of hydrogen gas released is tine (had a really hard time getting any of the bubbles to ignite). Another technique might be to hit the rust with some hydrocholoric acid in water - say about 2 oz./gallon - for a few minutes, rinse well (this concentration of acid shouldn't hurt pipes or septic system) - then put in the baking soda electrolyte bath. No matter which technique you use the water will turn orange if the rust is thick and while still useable I discarded it after about 1/2-1 hour's use. Have fun with this.
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